By escaping signals that normally constrain dividing cells, Cancer Stem Cells (CSCs) display unlimited proliferative potential. CSCs are thought to arise from the misregulation of normal stem cells that are capable of undergoing symmetric divisions and asymmetric divisions to allow stem cell self-renewal and the generation of a variety of terminally differentiated daughter cells. In order to develop chemotherapeutics to combat CSCs while avoiding damage to normal stem cells in healthy tissues, it will be crucial to understand what factors control the proliferation of both normal and tumorigenic stem cells. In addition, it will be especially important to understand how these cell types differ in responding to signals in their environment, and whether a tumor stem cell is able to initiate abnormal signaling both within the tumor mass itself, and in neighboring cells as part of its mechanism(s) for initiating tumorigenesis. Identifying the pathways that are required to confer hyperproliferative and metastatic potential upon tumor-initiating stem cells is made possible in the fruit fly Drosophila by a unique ability to generate mosaics of multiple genetic aberrations in mutant or wild type model systems, that makes Drosophila a powerful model system in which to model Cancer. In the proposed experiments, we will couple an ability to induce both benign and malignant tumors in Drosophila (by the co- expression of oncogenes and tumor suppressor mutant alleles) with the use of an exciting collection of pathway activity reporters to identify signal transduction pathways that may be abnormally coerced into supporting novel cellular outputs in oncogenically transformed stem cells. Further, by taking advantage of (1) a particularly advantageous tissue in the fly brain, the developing optic lobe, where actively proliferating cells are carefully controlled in a region of the brain where stem cells are undergoing transitions between symmetric and asymmetric division potential, and (2) a battery of useful markers for identifying the subcellular localization of key proteins required for controlling stem cell proliferative behaviors, we will be able to investigate whether oncogenes, like tumor suppressors, can trigger the formation of tumor-initiating stem cells by disrupting the acquisition and maintenance of cell polarity. Overall, the proposed experiments are expected to advance our understanding of (1) the factors that determine the proliferation rate of normal and tumor stem cells, including whether tumors can create their own microenvironment to bring about self-sufficiency in proliferation and cell survival control, (2) what differences in pathway activities may result from the activity of invasive vs. noninvasive tumor-initiating cells, (3) whether context-dependent pathway activity can lead to the creation of tumors with different phenotypes in vivo, and (4), if oncogenes can provide assistance in altering cell polarity, these experiments may identify a specific mechanism that can be manipulated by oncogenes to confer tumor- initiating capabilities upon normal stem cells. PUBLIC HEALTH RELEVANCE: This project aims to characterize the pathways that link oncogene-induced changes in signal transduction to cancer progression. Using a powerful Drosophila cancer model we will examine how cancer stem cells are regulated and test whether oncogenes alter cell polarity as part of a mechanism to induce tumorigenesis.